1. Field of the Invention
The present invention relates to a refrigerating cycle apparatus having multiple evaporators connected in parallel and operating under different evaporation pressures, where an evaporator working under the lowest evaporation pressure freezes a cold accumulating material. More particularly, the invention relates to a vehicular air-conditioner in which an evaporator operating under a high evaporation pressure air-conditions the interior of the vehicle while another evaporator working under a low evaporation pressure freezes a cold accumulating material so that when the vehicle is parked and inactive, the latent heat properties of the cold accumulating material are used to air-condition the vehicle interior.
2. Description of Related Art
An onboard vehicle air-conditioner of the above-mentioned type is described in Japanese Laid-Open Patent Publication No. Sho 62-149509. This device has a refrigerating cycle compressor equipped with a primary and a secondary inlet port independent of each other. The two inlet ports correspond to a primary and a secondary group of compressor cylinders. The primary inlet port is connected to the outlet of an evaporator for air-conditioning the driver's compartment of a truck, and the secondary inlet port is linked to the outlet of a cold accumulating evaporator which air-conditions the driver's nap space on the truck.
A constant-pressure expansion valve is installed upstream of the evaporator for the nap space of the truck. In operation, the constant-pressure expansion valve keeps the pressure of the cold accumulating evaporator for the nap space at 1.0 to 1.2 kg/cm.sup.2 (the evaporation temperature is between -10.degree. C. and -8.degree. C. for refrigerant R-12 (dichlorodifluoromethane)). The evaporator freezes the cold accumulating material while the vehicle is running, whereby cold potential is accumulated. When the vehicle is parked, air chilled by the cold accumulating material is sent into the nap space. In this manner, the nap space is air-conditioned without having the compressor actuated by the engine of the vehicle.
According to the present inventors' experiments and studies, the proposed apparatus above is subject to irregularities in the behavior of the refrigerant within the refrigerating cycle in connection with the freezing of the cold accumulating material. The irregularities, not mentioned in the above-cited publication, are as follows:
In the above device, the freezing of the cold accumulating material makes the temperature inside the cold accumulating evaporator for the nap space equal to the temperature of a decompressed two-phase (gas/liquid) refrigerant. The liquid refrigerant is unable to absorb heat from the cold accumulating material and is thus forwarded in its liquid form, i.e., without being evaporated, to the outlet side. As a result, when the cold accumulating material is completely frozen (i.e., cold accumulating operation completed), the liquid refrigerant remains stagnant throughout the cold accumulating evaporator.
When the compressor is at rest with the cold accumulating operation completed, the cold accumulating material is at about 0.degree. C. and the refrigerant pressure inside the cold accumulating evaporator for the nap space is approximately 0.2 MPa. Where the outside temperature is illustratively 25.degree. C., the refrigerant pressure outside the cold accumulating evaporator is 0.6 MPa. The resulting difference in pressure between the cold accumulating evaporator for the nap space and the evaporator environment would cause the refrigerant to enter the cold accumulating evaporator and stay there. That eventuality appears to be forestalled by the proposed apparatus having a solenoid valve installed upstream of the cold accumulating evaporator and a check valve located downstream thereof. However, leaks through the valves make it impossible completely to stop the entry of the refrigerant into the cold accumulating evaporator for the nap space.
The resulting shortage of the refrigerant in the evaporator for the driver's compartment can render the evaporator performance insufficient for air-conditioning. At the same time, inside the compressor, both the refrigerant and the lubricating oil that circulates through the refrigerating cycle remain stagnant in the cold accumulating evaporator. A shortage of oil reflux as a result of this can lead to lubrication irregularities.